Electrodynamic speaker



May 24, 1932. I R. T, KlNGSFORD 1,859,518

ELECTRODYNAMIC SPEAKER Filed May 17, 1950 Patented May 24, 1932 entree mm PATENT orrica RUSSELL T. KIN GSFOBD, OF WYNGQTE, PENNSYLVANIA, ASSIGNOR TO ATWATER KENT MANUFACTURING COMPANY, F PHILADELPHIA, PENNSYLVANIA, A CORPORA- TION OF PENNSYLVAJ. IA

I ELECTRODYNAMIC SPEAKER Application filed May 17, 1930 Serial No. 453,130.

My invention relates to telephonic apparatus of the electro-dynamic type, and particularly such as may be utilized as loud speakers either in radio reception or for other purposes.

In accordance with my invention the electro-magnetic field structure comprises a casing or pot having a central core terminating in a pole piece disposed centrally in a circular aperture in an outer pole plate structure which is held, with its aperture concentric with the central pole piece to form an air gap of uniform length, against the end of the pot, whether or not'flanged, to prevent its displacement with respect to the core or pole piece without recourselto a spacing ring or other centering means.

Further in accordance with my invention, the outer pole plate structure comprises a pole plate having secured thereto, preferably on the inner side thereof, a. second plate, also of magnetizable material, effecting reduction in magnetic reluctance and at the same time cheapening the structure; and more particularly the inner plate approacheslthe inner pot Wall suficiently closely to reduce mag netic reluctance, whi e their distance apart may be such that if the outer pole plate structure were shifted, it would at its air gap aperture strilre the voice coil, or even the inner pole piece, without the edge of the inner plate reaching or contacting with'the inner wall of the pot.

My invention resides instructure and features of the character hereinafter described and claimed. 7 a

For an illustration of some of the various forms my structure may take, and for an understanding of the invention in general, reference is to be had to the accompanying drawings, in which: 3

Fig. 1 is a vertical sectional view of an electro-dynamic loud speaker of the cone type embodying my invention; 7

Fig. 2 is a side elevational view of my novel pot with its central core;

Fig. 3 is a top shown in Fig. 2;

Fig. l is abottom plan view of the composite outer pole plate structure;

plan view of the structure Fig. 5 is a side elevational view of the structure shown in Fig. 4;

Fig. 6 is afragmentary view in section, illustrating a modification in which the pot flange is omitted; i i

Figs. 7 and 8 illustratethe strips from which are procured respectively rectangular and circular blanks for pot formation.

Referring to Figs. 1. to 5 inclusive, 'P is a casing or pot of magnetic material upon whose bottom 1 is secured the inner core 2,

held in fixed and non-adjustable position with respect to the pot by the'screw or bolt 3 threaded into the core 2 after passing through the supplemental bottom plate l of nagnetizable material, utilized when'desir- Surrounding the core 2 is the field winding C, energized by direct or rectified alternating current, to produce a substantially unfluctuating magnetic field in the air gap between the circular inner pole piece I, on

the core 2, and the inner wall of the'aperture 5 in the outer pole plate structure 0, having adjacent its outer edge holes 6 through which and the flange 7, uponthe pot P,ex-

tend bolts or screws 8, which securely hold the pole plate structure 0 fixedly upon the pot P with the aperture 5 truly concentric with the pole piece I, without recourse to or need for a spacing or centering ring or disc or othermeans for locating'structure O with respect to pole I. p

The plate structure 0 maybe centered with respect to the inner pole I in any suitable way, as by introduction into the air gap of a gauge or gauge elements, and when so centralized the bolts 8, which preferably have substantial clearance in the holes 6, are tightened. I

The outer pole plate structure may be unitary, or, and preferably, as; indicated, is composite, comprising the larger plate Shaving secured thereto by rivets 10, or equivalent, the smaller and inner plate 11, both plates having registering apertures.

When the parts are in the assembled position described, the coil C is held in place against the bottom washer 12 of insulating material by the upper washer 13 of pasteclosely approach the inner wall'of the pot P, as indicated in Fig. 1, to maintain low magnetic reluctance. Nevertheless, the spacing may. be such that in event of displacement of outer pole plate structure the wall of the aperture would first engage the movable coil S, oreven the periphery of the inner pole piece Lbefore touching the pot P.

The screws .8 also secure to the pot structure the sheet metal housing 16 having suitably large openings 17, and having the outwardly, turned circular flange 18 terminatingwith the forwardly extending flange 19, forming a channel within which isydisposed the ring 20' of felt, paper or other suitable material. Upon the Washer 20 lies the annular disc 21 of flexible cloth or the like to whose inner flange 22 is attached the outer end of the conical diaphragm D of paper or other suitable material. Overlying the member 21 is'a metal ring or washer 23 held by the screws 24. v

The coil S, traversedby signals or soundrepresenting current, is disposed in one or more layers upon the coil form or support .F between whose forward ends and the-sheet metal flange 25 is held the inwardly turned end, 26 of the cone D which overlies the conical'flange 27 integral with the flange 25, which in turn is integral with the spring spider Z ,of aluminum or other suitable material, sccured at its center by screw 28 to the lug or projection 29 upon the innerrpole piece I- Withthe screws 24 loose, the cone Dis first centered by means of removable spacers inserted through apertures in spider Z between the inside of the coil form F and the outside of the inner pole piece I, and then by tightening the screw 28 the spider Z is secured to the inner pole piece I, whereupon the screws 24 are tightened with assurance that the coneas a whole is properly positioned or centered.

The voice coil leads L extend from the moving coil system to suitable terminals 30;

and the leads 31, 31 from the coil C extend to similarly-fixed terminals 32., The terminals are secured upon suitable insulating material mounted upon the housing 16, and enclosed in a metal cap 33, secured to the housing, and having a neck 34 through which extends a cable 35, in which are disposed the four conductors connecting with the two of width indicated terminals 30 and the two terminals 32 within the cap 33, between whose inner side and the terminals, their mountings and connections may be interposed a paper or other suitable covering 36. r l g V A pot of the character illustrated in Figs. 1,2 and 3 is drawn to form by a suitable die operating upon an oblong cold blank, such as indicated at B, Fig. 7, stamped or cut from strips of stock 37 having suitable magnetic and die-working'properties. Each blank B is substantially longer than its width for producing a pot of the form or'proportions indicated in Figs. 2 and 3. In forming the pot, there is left a f-shaped notch N on each of opposite sides, terminating at or in the flanges 7, which, by suitable formation of the die, may have the straight sides 38. After the pot-forming operation, there gen erally remains a more or less ragged edge around the flange 7 and straight sides 38, which is readily removed by a trimming or finishing die. The forward faces of the flanges, engaged by the outer pole plate structure, may be suficiently trued by grinding or equivalent operation. The width of the plate 9, of the outer pole plate structure O, between its opposite parallel sides 39, is substantially the width between the straight sides 38, 38 of the pot structure. The plates 9 may be stamped from material of that width, and the curved ends preferably conform with the curved flanges 7 of the pot.

Similarly, the, inner plate 11, of the outer. pole plate structure 0, has parallel straight sides; 40, parallel to the straight sides 39 of the-outer plate-9, and in general'parallel to the straight sides 38, 38 of the pot. The

plates 11 may be stamped from strip stock between the straight sides 40, 40.

Fig. 8-represents a strip of stock 41 from 'which. are stamped circular pot blanks B1 in customary prior practice. It is evident that aconsiderable portion of the blank stock 41 is wasted, since all the area of the strip 41 between neighboring blanksBl is waste, and in addition there is waste at the regions 42, due to the fact that satisfactorily to stamp a circular blank from a strip, the blank must fall short on each side an amount equivalent. to approximately the thickness of the stock.

In contrast, when using a rectangular blank B, Fig. 7, the waste in cutting blanks from the stock is entirely eliminated. The difference in waste in the two cases is so substantial that by utilizing blocks B of the same weight as circular blanks E1, the thickness of the stock for the blanks Bmay be so much greater, generally thicker, with such resultantincrease in thickness of the walls of the formed pot P that the magnetic reluctanceof the-circuit is so much lessened-that the amount. of copper inthe winding of the ion field coil C may be materially reduced, in some cases to the order of one-third. In drawing or forming pots from circular blanks B1, two forming operations are required, followed by a trimming operation. With rectangular blanks, such as B, but a single forming operation is necessary followed by the usual trimming operation.

By way of comparison, it may be stated that circular blanks B1, for a given pot structure, having a diameter of 8 inches, are stamped from stock 8 inches wide and about inch thick, while, in accordance with my invention for an equivalent structure, the blanks B1 may be 9 inches long and 5 1 wide and about 50% thicker than in the case of the blanks Bl.

Because of suitable ratio of length to width of a blank B, there may be produced in a single operation a pot which is deep, as illus trated, or which may, if desirable, be even deeper. The pot in accordance with my invent on is deep in the sense that it is as deep as pots heretofore drawn or formed from circular blanks as B1, in at least two operations. By recourse to a rectangular blank whose length is suitably great with respect to its width, a pot of practically any depth may be procured in a single operation. 1 This results from the fact that during the first part of the relative movement of the die members with respect to each other, the effect is to draw or work the metal; while in the remainder of the movement the action is practically merely bending, forming orfolding. In consequence, my pot may be described as one which is deep, whose bottom portion is characterized as drawn, and whose upper portion is characterized as merely formed.

The aforesaid advantages arise in the case where the pot structure as a whole is formed of a single pot element whose depth is relatively great, as approximately equal to or greater than its diameter, particularly when using a blank B considerably longer than its width. In a pot of this structure, the notch N is deep, and terminates at the open end of the pot at a level adjacent that of the air gap for the movable coil.

lVhile, as indicated in Fig. 1, the leads 31 from the field coil C may extend through the outer pole plate structure 0, they may extend I outwardly through one of the notches N in register with which, for the purpose, there may be a notch 9a in the outer pole plate 9, as indicated in Figs. 4 and 5.

While the pot P may have flanges 7 above described, they may be omitted, as indicated in Fig. 6, and the outer pole plate structure 0 may abut against the squared end 43 of the pot, and there held firmly, without recourse to a spacing ring or equivalent centering means, by bolts 44 passing through an extended bottom plate 4:, and through the plate 9 and housing member 16.

What I clams; a My I 1., In telephonic apparatus of the character described, the combination with a pot, a

central core and magnetizing winding,'of

outer pole plate structure comprising a plate secured to the pot, and a second plate secured to said plate on the inner side thereof, said plates having registering apertures forming with said central core an air gap, said inner plate terminating short of the wall of said pot.

2. In telephonic apparatus of tl'lB'ChfiIilC- ter described, a single pot element closed at its one end and open at the other, afield core a V disposed in said pot extending from its bottom and terminating approximately at its open end, a magnetizing winding on'said core, notches formed in opposite sides of said pot element extending to itsopen end,and pole plate structure secured to the open end 4 of said pot element between said notches, and

having an aperture receiving said field core to form an air gap.

3. Intelephonic apparatus of the charac-h ter described, a single pot element closed at its one end and open at the other, a field core. disposed in said pot extending fromits bot tom and terminating approximately at its open end, a magnetizing winding on saidcore, notches formed in" opposite sides of said pot element extending to its open end, laterally turned flanges integral with said pot element at its open end between said notches, and pole plate struoture'secured to said flanges and, having an aperture receiving said field core' to form an air gap. V

' 4. In telephonic apparatus of the character described, a single pot element closed at its one end and open at the other, a field core, disposed in said pot extending from its bottom and terminating approximately at its open end, a magnetizing winding on sa d core, notches formed in opposite sides of said pot element extending to its open end, later: ally turned flanges integral'with said pot ele-" ment atits open end betweensaid'notches, and pole plate structure secured to said flanges and having an aperture receiving sa d field core to form an air gap, said flanges and said pole plate structure having substantially coinciding parallel straight sides.

5. In telephonic apparatus of the character described, a pot element having flange structure at its open end, afield core disposed in said pot, a magnetizing winding on said core, and outer pole plate structure comprising a plate secured to the flange on said pot element,iand an inner plate secured to said first A- I rssa srs casing, a stud pole Within-said windingand secured in fixed position with respectto said vcasing, a singlepole plate structure of mag- ,netizable material engaging and adjustable "'5zupon the open end of said casing and havingfa central aperture formingwith said stud p 7 pole an' air gap, the relationrof said aperture "with respect to said stud pole depending solely upon the adjusted position of said sin- 7 10 gle pole plate structure upon the end ofsaicl casing, and means for holding said pole plate structure in adjusted position in frictionalengagement with the open end of said casing toiprevent deformationof said air gap.

' 7. In telephonic, apparatus of the character described, a unitary potwshaped casing of magnetiz able material, a Winding within said casing, .a stud pole Within said Winding and secured in fixed position Withrespect to said '2 casing, a single pole plate structure of magnet-izable material engagingrand adjustable upon the open end ofsaid casingand having a central aperture forming With said stud pole an air gap, therelation of said 1:25 aperture with respect to said stud pole depending solely upon the adjusted position of saidpole plate structure upon the end of said pole casing,,means for holding said plate structure in adjusted posit-ion in frictional "$0 engagement with the open endof said casing ,to prevent deformation of said air gap, a diaphragm, and a voice coil attached to said diaphragm disposed in said air gap.

8. In telephonic apparatus of the character 75 described, :a single .pot element closed at one end and open at the other, a field core disiposed insaid pot extending from its bottom and terminating approximately at its open end, a magnetizing Winding on said. core, 2 notches formed in opposite sides of said pot element extending to its open end, pole plate structure having an aperture receiving-said field score toformwan air gap, and means for slidably securing said pole plate structure in 1'545 frictional engagementwith the open end of said potelement between said notches to prevent ideformationnof said air gap.

9. Intelephonic'apparatus of the character described, a singlepot element closed at one 9 end and openiattheother, a field core disposed in said pot extending from-its bottom' and terminating approximately at its open end, a magnetizing Windingv onsaid core, laterally turned .fiange 7 structure integral 1 .With said pot elementat its open end, a single pole platestructure slidably engagingsaid flange structure and having an aperture receiving said fieldcoreto form an airgap, and means for securing said pole plate structure 'in frictional engagement with said flange structure to prevent deformation of said ,air

pe a RUSSELL T. KINGSFOBD. 

